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    <script>
        /* 
            Symbol : 符号、象征
            字符串： apple  apple  orange  apple
            作用 : 标识字符串的唯一性
        
            基本数据类型 ：number string boolean object(null) undefined 
            ES 6 : 新增 symbol
        */
        // 1. 创建    
        let address1 = Symbol('郑州');
        let address2 = Symbol('郑州');

        console.log(address1);
        console.log(address1 === address2);
        console.log("郑州" === "郑州");

        // 2. 数据类型是 symbol   而不是对象
        console.log(typeof address1);  // symbol

        // 3. 获取 symbol 的描述 
        console.log(address1.description);

    </script>

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